(1) Field of the Invention
The present invention relates to a packing can. More particularly, the present invention relates to a packing can which has an excellent resistance against deformation caused by the reduction of pressure at the cooling step after filling the can with contents or during the subsequent storage, and which makes it is made possible to reduce the thickness of the blank used to form the can.
(2) Description of the Related Art
Metal is mainly used for a packing can and sometimes, a resin material is used. In the case of utilizing a metal sheet, a three-piece can is prepared by forming metal sheet into a cylindrical shape, joining confronting edge portions by welding, bonding or soldering to form a can barrel having a side seam and thereafter wrap-seaming both the ends of the can barrel with top and bottom lids. Alternately, a two-piece can is formed by deep-drawing or further ironing the metal sheet into a bottomed can barrel and wrap-seaming the top end of the bottomed can barrel with a lid.
In these packing cans, efforts have been made to reduce the thickness of the blank as much as possible to lower the material cost of the can and reduce the weight of the can per se. However, reduction of the thickness of the blank should naturally result in reduction of the mechanical strength of the can barrel. Particularly, during the cooling step after filling the can with its contents or during the subsequent storage or transportation thereof, conspicuous deformation (profile deformation) of the can barrel is caused by reduction of the internal pressure. Moreover, in canned products, during handling or transportation, collision of cans cannot be avoided, and deformation of can barrels is also caused by such collision.
If deformation is caused in a can barrel of a packing can, the appearance of the product is degraded and the commercial value is lost, and furthermore, coating defects such as pinholes, cracks and peels are caused in inner and outer protecting coating layers of the metal sheet and such troubles as corrosion, elution of the metal and leakage by pitting are readily caused.
As the conventional means for reinforcing the can barrel member, there is known a method in which beads are formed in the circumferential direction of the can barrel and beads are formed in the direction of the can height (the axial direction of the can).
If beads are formed on a barrel member, the above-mentioned deformation is considerably effectively prevented, but in the case where circumferential beads are formed on the front face of the can barrel member, the increase of the deformation load by the external pressure (the increase of the strength against the deformation by the external pressure) is about 2 times at the maximum, as compared with the case of a similar can having no beads formed. Accordingly, even if the thickness of the blank is considerably reduced, the object of completely preventing deformation by reduction of the pressure is not sufficiently attained.
Furthermore, if beads are formed on a can barrel, undulations appear on the printed outer surface and the appearance or commercial value of the can is lowered and coating defects are also caused on the inner surface of the can, and a defect of increase of the metal exposure (ERV value) attractive. Accordingly, in beaded can barrels now practically used, only circumferential beads are formed at a limited part of the can barrel.